1. Field of the Invention
This invention relates to the storage and transmission of one-bit (or “delta-sigma modulated) data, such as one-bit digital audio signals.
2. Description of the Prior Art
A convenient way of storing one-bit digital audio signals with currently available equipment is to multiplex groups of bits of the one-bit signal into data words, and then to record the data words on conventional multi-bit PCM recording equipment. For example, a one-bit signal at 64 fs (where fs is, for example, 48 kHz) can be treated in this way by multiplexing 64 successive bits of the one-bit signal into 4×16-bit words, which can then be recorded on two stereo channels of a standard so-called AES/EBU digital audio recorder.
However, if there is a replay problem and the AES/EBU recorder mutes, its output goes to a continuous stream of digital zeroes. In a PCM system, a continuous stream of zeroes would be decoded as silence. However, in a one-bit data stream, a continuous stream of zeroes would be decoded as a very large magnitude audio signal—in fact, larger than the peak signal that most one-bit systems are designed to handle.
Similar problems can occur when one-bit data is stored or transmitted without necessarily reformatting the data into data words; if the signal disappears or mutes to a steady sequence of the same bit value, then this is equivalent to a very loud noise (or, more generally, a very large signal) in the one-bit system.